Well, I think Windows would know what "type" of key it is, the same way it would know what type of Windows you are doing the upgrade on (Professional, Home, etc). There is no reason to think Microsoft can't tell it's a 3-license key for the number itself.
They can't. Ever try to activate a family pack key by phone? You would think that they would be able to identify it as a Family Pack key, and "know" that it's allowed three activations. But when the electronic voice asks how many computers is it installed on, if you answer "three", it tells you that you've installed it too many times, and to buy a new copy.
You MUST not say anything when you call the phone activation, and WAIT until you get a human to pick up on the line, then explain to them that you have a family pack key, and then you can get an activation.
The family pack keys only show up as Win7 Home Premium Retail Upgrade. They don't show up as anything special, as far as I know.